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Abstract:

Disclosed is a catalyzed soot filter with layered design wherein the
first coating of the filter comprises an oxidation catalyst comprising
platinum (Pt) and optionally palladium (Pd), wherein the second coating
of the filter comprises an oxidation catalyst comprising Pd and
optionally Pt, wherein the Pt concentration in the second coating is
lower than the Pt concentration in the first coating, and wherein the
weight ratio of Pt:Pd in the second coating is in the range of from 1:1
to 0:1; and wherein the first coating and the second coating are present
on the wall flow substrate at a coating loading ratio in the range of
from 0.25 to 3, calculated as ratio of the loading of the first coating
(in g/inch3 (g/(2.54 cm)3)): loading of the second coating (in
g/inch3 (g/(2.54 cm)3)).

Claims:

1. A catalyzed soot filter, comprising a wall flow substrate comprising
an inlet end, an outlet end, a substrate axial length extending between
the inlet end and the outlet end, and a plurality of passages defined by
internal walls of the wall flow filter substrate; wherein the plurality
of passages comprise inlet passages having an open inlet end and a closed
outlet end, and outlet passages having a closed inlet end and an open
outlet end; wherein a given inlet passage, an adjacent outlet passage,
and the internal wall between said inlet and said outlet passage define
an overall passage; wherein the internal walls of at least 20% of the
overall passages are at least partially coated with a first and a second
coating; wherein the internal wall of a given at least partially coated
overall passage comprises the first coating that extends from the open
inlet end to a first coating end, thereby defining a first coating
length, wherein the first coating length is x % of the substrate axial
length, with 20.ltoreq.x≦100; wherein said internal wall of said
overall passage further comprises the second coating located downstream
of the first coating, said second coating having a second coating length
of y % of the substrate axial length, with 20.ltoreq.y≦100;
wherein the first and the second coating overlap in length by at least
20% of the substrate axial length; wherein the first coating comprises an
oxidation catalyst comprising platinum (Pt) and optionally palladium (Pd)
and wherein the weight ratio of Pt:Pd in the first coating is in the
range of from 1:0 to greater than 1:1; wherein the second coating
comprises an oxidation catalyst comprising Pd and optionally Pt, wherein
the Pt concentration in the second coating is lower than the Pt
concentration in the first coating and wherein the weight ratio of Pt:Pd
in the second coating is in the range of from 1:1 to 0:1; wherein the
first coating and the second coating are present on the wall flow
substrate at a coating loading ratio in the range of from 0.25 to 3,
calculated as ratio of the loading of the first coating (in g/inch3
(g/(2.54 cm)3)): loading of the second coating (in g/inch3
(g/(2.54 cm)3)).

2. The catalyzed soot filter according to claim 1, wherein the second
coating extends from the open inlet end to a second coating end, thereby
defining the second coating length of y % of the substrate axial length.

3. The catalyzed soot filter according to claim 1, wherein the second
coating extends from the open outlet end to a second coating end, thereby
defining the second coating length of y % of the substrate axial length.

4. The catalyzed soot filter of claim 1, wherein x is in the range of
from 20 to 80.

5. The catalyzed soot filter of claim 1, wherein the coating loading
ratio is in the range of from 0.75 to 1.25.

6. The catalyzed soot filter of claim 1, wherein the loading of the first
coating is in the range of from 0.05 to 1, and wherein the loading of the
second coating is in the range of from 0.05 to 1.

7. The catalyzed soot filter of claim 1, wherein in the first coating,
the weight ratio of Pt:Pd is in the range of from 1:0 to 2:1.

8. The catalyzed soot filter of claim 1, wherein in the first coating,
the weight ratio of Pt:Pd is 1:0.

9. The catalyzed soot filter of claim 1, wherein in the second coating,
the weight ratio of Pt:Pd is in the range of from 1:2 to 0:1.10. The
catalyzed soot filter of claim 1, wherein in the second coating, the
weight ratio of Pt:Pd is 0:1.

10. The catalyzed soot filter of claim 1, wherein the weight ratio of the
sum of the weights of Pt and optionally Pd in the first coating to the
sum of the weights of Pd and optionally Pt in the second coating is in
the range of from 1:6 to 10:1.

11. The catalyzed soot filter of claim 10, wherein the weight ratio of
the sum of the weights of Pt and optionally Pd in the first coating to
the sum of the weights of Pd and optionally Pt in the second coating is
in the range of from 1:6 to 2:1.

12. The catalyzed soot filter of claim 11, wherein in the first coating,
the weight ratio of Pt:Pd is 1:0 and the concentration of Pt is in the
range of from 0.5 to 1 g/ft3 (g/(30.48 cm)3), and wherein in
the second coating, the weight ratio of Pt:Pd is 0:1 and the
concentration of Pd is in the range of from 0.5 to 3 g/ft3 (g/(30.48
cm)3).

13. The catalyzed soot filter of claim 10, wherein the weight ratio of
the sum of the weights of Pt and optionally Pd in the first coating to
the sum of the weights of Pd and optionally Pt in the second coating is
in the range of from 2.4:1 to 10:1.

14. The catalyzed soot filter of claim 13, wherein in the first coating,
the weight ratio of Pt:Pd is in the range of from 1:0 to 1:1, and the
concentration of Pt is in the range of from 5 to 100 g/ft3 (g/(30.48
cm)3), and wherein in the second coating, the weight ratio of Pt:Pd
is in the range of from 0:1 to 1:1, and the concentration of Pd is in the
range of from 1 to 30 g/ft3 (g/(30.48 cm)3).

15. The catalyzed soot filter of claim 1, wherein the oxidation catalyst
comprised in the first coating consists of Pt and optionally Pd and the
oxidation catalyst comprised in the second coating consists of Pd.

16. The catalyzed soot filter of claim 1, wherein the first coating and
the second coating comprise at least one porous support material for the
respective platinum group metal(s), wherein the at least one porous
support material of the first coating comprises a ceria-zirconia material
consisting of CeO2: 45 wt %, ZrO2: 43.5 wt %, La2O3:
8 wt %, Pr6O11: 2 wt %, and HfO2: 1.5 wt %, and wherein
the at least one porous support material of the second coating comprises
a ceria-zirconia material consisting of CeO2: 45 wt %, ZrO2:
43.5 wt %, La2O3: 8 wt %, Pr6O11: 2 wt %, and
HfO2: 1.5 wt %.

17. The catalyzed soot filter of claim 16, wherein the support material
of the first coating comprises Al2O3 and wherein the support
material of the second coating comprises Al2O.sub.3.

18. The catalyzed soot filter of claim 1, wherein the wall flow substrate
has a porosity in the range of from 38 to 75, determined according to
mercury porosity measurement according to DIN 66133.

19. The catalyzed soot filter of claim 1, comprised in a system for
treating a diesel engine exhaust stream, the system further comprising an
exhaust conduit in fluid communication with the diesel engine via an
exhaust manifold, and further comprising one or more of the following in
fluid communication with the catalyzed soot filter: a diesel oxidation
catalyst (DOC), a selective catalytic reduction (SCR) article, an NOx
storage and reduction (NSR) catalytic article.

20. The catalyzed soot filter of claim 19, arranged downstream of the
DOC.

21. The catalyzed soot filter of claim 1 for use in a method of treating
a diesel engine exhaust stream, the exhaust stream containing soot
particles, said method comprising contacting the exhaust stream with the
catalyzed soot filter.

22. A process for manufacturing a catalyzed soot filter of claim 1,
comprising the steps of (i) providing a wall flow substrate, said wall
flow substrate comprising an inlet end, and outlet end, a substrate axial
length extending between the inlet end and the outlet end, and a
plurality of passages defined by the internal walls of the wall flow
substrate; wherein the plurality of passages comprise inlet passages
having an open inlet end and a closed outlet end, and outlet passages
having a closed inlet end and an open outlet end; wherein a given inlet
passage, an adjacent outlet passage, and the internal wall between said
inlet and said outlet passage define an overall passage; (ii) applying a
first coating to at least part of the internal walls of at least 20% of
the overall passages such that the first coating extends from the inlet
end to a first coating end whereby a first coating length is defined,
wherein the first coating length is x % of the substrate axial length,
with 20.ltoreq.x≦100, thereby adjusting the loading of the first
coating to a predetermined value, said first coating comprising an
oxidation catalyst comprising platinum (Pt) and optionally palladium (Pd)
wherein the weight ratio of Pt:Pd in the first coating is in the range of
from 1:0 to greater than 1:1; (iii) applying a second coating to at least
part of the internal walls of said overall passages downstream of the
first coating, said second coating having a second coating length of y %
of the substrate axial length, with 20.ltoreq.y≦100, so that the
first and the second coating overlap in length by at least 20% of the
substrate axial length; thereby adjusting the loading of the second
coating to a predetermined value such that the first coating and the
second coating are present on the wall flow substrate at a coating
loading ratio in the range of from 0.25 to 3, calculated as ratio of the
loading of the first coating (in g/inch3 (g/(2.54 cm)3)):
loading of the second coating (in g/inch3 (g/(2.54 cm)3)), said
second coating comprising an oxidation catalyst comprising Pd and
optionally Pt, wherein the Pt concentration in the second coating is
lower than the Pt concentration in the first coating and wherein the
weight ratio of Pt:Pd in the second coating is in the range of from 1:1
to 0:1.

23. The process of claim 22, wherein step (iii) is carried out before
step (ii) and wherein the second coating is applied such that it extends
from the open inlet end to a second coating end, thereby defining the
second coating length of y of the substrate axial length.

24. The process of claim 22, wherein step (iii) is carried out before,
simultaneously with or after step (ii) and wherein the second coating is
applied such that it extends from the open outlet end to a second coating
end, thereby defining the second coating length of y % of the substrate
axial length.

25. A system for treating a diesel engine exhaust stream, the system
comprising an exhaust conduit in fluid communication with the diesel
engine via an exhaust manifold; a catalyzed soot filter of claim 1; and
one or more of the following in fluid communication with the catalyzed
soot filter: a diesel oxidation catalyst (DOC), a selective catalytic
reduction (SCR) article, a NOx storage and reduction (NSR) catalytic
article.

26. The system of claim 25, wherein the catalyzed soot filter is arranged
downstream of the DOC.

28. The method of claim 27, further comprising directing the exhaust
stream resulting from the DOC or from the catalyzed soot filter through a
selective catalytic reduction (SCR) article.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119(e) to
U.S. Provisional No. 61/485,654, filed May 13, 2011, the disclosures of
which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

[0002] The present invention relates to a catalyzed soot filter, in
particular for the treatment of Diesel engine exhaust, with a layered
design which ensures soot particulates filtration, assists the oxidation
of carbon monoxide and unburned hydrocarbons, and produces low NO2
emissions during normal engine operations and active regeneration events.

BACKGROUND

[0003] Diesel engine exhaust is a heterogeneous mixture which contains not
only gaseous emissions such as carbon monoxide ("CO"), unburned
hydrocarbons ("HC") and nitrogen oxides ("NOx"), but also condensed phase
materials, i.e. liquids and solids, which constitute the so-called
particulates or particulate matter. Emissions treatment systems for
diesel engines must treat all of the components of the exhaust to meet
the emission standards set by the various regulatory agencies throughout
the world.

[0004] The total particulate matter emissions of diesel exhaust contain
three main components. One component is the solid, dry, solid
carbonaceous fraction or soot fraction. This dry carbonaceous fraction
contributes to the visible soot emissions commonly associated with diesel
exhaust. A second component of the particulate matter is the soluble
organic fraction ("SOF"). The SOF can exist in diesel exhaust either as a
vapor or as an aerosol (fine droplets of liquid condensate) depending on
the temperature of the diesel exhaust. It is generally present as
condensed liquids at the standard particulate collection temperature of
52° C. in diluted exhaust, as prescribed by a standard measurement
test, such as the U.S. Heavy Duty Transient Federal Test Procedure. These
liquids arise from two sources: (1) lubricating oil swept from the
cylinder walls of the engine each time the pistons go up and down; and
(2) unburned or partially burned diesel fuel. The third component of the
particulate matter is the so-called sulfate fraction, which is formed
from small quantities of sulfur components present in the diesel fuel.

[0005] Catalyst compositions and substrates on which the compositions are
disposed are typically provided in diesel engine exhaust systems to
convert certain or all of these exhaust components to innocuous
components. For instance, oxidation catalysts that contain platinum group
metals, base metals and combinations thereof facilitate the treatment of
diesel engine exhaust by promoting the conversion of both unburned
hydrocarbons (HC) and carbon monoxide (CO) gaseous pollutants, and some
proportion of the particulate matter through oxidation of these
pollutants to carbon dioxide and water. Such catalysts have generally
been disposed on various substrates (e.g. honeycomb flow through monolith
substrates), which are placed in the exhaust of diesel engines to treat
the exhaust before it vents to the atmosphere. Certain oxidation
catalysts also promote the oxidation of NO to NO2.

[0006] In addition to the use of oxidation catalysts, diesel particulate
filters are used to achieve high particulate matter reduction in diesel
emissions treatment systems. Known filter structures that remove
particulate matter from diesel exhaust include honeycomb wall flow
filters, wound or packed fiber filters, open cell foams, sintered metal
filters, etc. However, ceramic wall flow filters, described below,
receive the most attention. These filters are capable of removing over
90% of the particulate material from diesel exhaust. Typical ceramic wall
flow filter substrates are composed of refractory materials such as
cordierite or silicon-carbide. Wall flow substrates are particularly
useful to filter particulate matter from diesel engine exhaust gases. A
common construction is a multi-passage honeycomb structure having the
ends of alternate passages on the inlet and outlet sides of the honeycomb
structure plugged.

[0007] This construction results in a checkerboard-type pattern on either
end. Passages plugged on the inlet axial end are open on the outlet axial
end. This permits the exhaust gas with the entrained particulate matter
to enter the open inlet passages, flow through the porous internal walls
and exit through the channels having open outlet axial ends. The
particulate matter is thereby filtered on to the internal walls of the
substrate. The gas pressure forces the exhaust gas through the porous
structural walls into the channels closed at the upstream axial end and
open at the downstream axial end. The accumulating particles will
increase the back pressure from the filter on the engine. Thus, the
accumulating particles have to be continuously or periodically burned out
of the filter to maintain an acceptable back pressure.

[0008] Catalyst compositions deposited along the internal walls of the
wall flow substrate assist in the regeneration of the filter substrates
by promoting the combustion of the accumulated particulate matter. The
combustion of the accumulated particulate matter restores acceptable back
pressures within the exhaust system. These processes may be either
passive or active regeneration processes. Both processes utilize an
oxidant such as O2 or NO2 to combust the particulate matter.

[0009] Passive regeneration processes combust the particulate matter at
temperatures within the normal operating range of the diesel exhaust
system. Preferably, the oxidant used in the regeneration process is
NO2 since the soot fraction combusts at much lower temperatures than
those needed when O2 serves as the oxidant. While O2 is readily
available from the atmosphere, NO2 can be actively generated though
the use of upstream oxidation catalysts that oxidizes NO in the exhaust
stream.

[0010] In spite of the presence of the catalyst compositions and
provisions for using NO2 as the oxidant, active regeneration
processes are generally needed to clear out the accumulated particulate
matter, and restore acceptable back pressures within the filter. The soot
fraction of the particulate matter generally requires temperatures in
excess of 500° C. to burn under oxygen rich (lean) conditions,
which are higher temperatures than those typically present in diesel
exhaust. Active regeneration processes are normally initiated by altering
the engine management to raise temperatures in front of the filter up to
570-630° C.

[0011] During the passive regeneration on current state of the art
catalyzed soot filter, the NO2 consumed during the oxidation of soot
can be produced again by the catalyst assisted oxidation of NO along the
channel of the catalyzed soot filter. In order to provide sufficient
NO2 to oxidize soot and avoid frequent active soot regenerations,
Pt-rich washcoats have been applied on the soot filter material. However,
such Pt-rich washcoats raise concerns due to risk of producing a high
amount of NO2 which would exit the catalyzed soot filter without
being used for the oxidation of soot. The NO2 exiting the catalyzed
soot filter can be emitted in the atmosphere only if its concentration
fulfills the requirements of the air regulation limits, otherwise its
concentration has to be reduced or the NO2 converted by means of
further downstream catalysts such as NOx traps and/or catalysts able to
selectively reduce NOx in presence of urea, ammonia or hydrocarbons. The
need of abating the NO2 emission is not only limited to the normal
operation of a diesel engine but also during the so called active
regenerations. In fact, during the high temperature oxidation of soot by
oxygen, NO2 produced on the Pt-rich washcoat can not be fully
consumed by reaction with soot.

[0012] EP-A-1 541 219 discloses a catalyzed soot filter which would
simultaneously remove soot and NOx by combination of NOx storage
catalysts with the soot filter. This solution is however disadvantageous
in that it additionally requires the use of another precious metal, e.g.
Ag and/or base metal oxides, for the storage and conversion and/or
release of NOx or to limit the NO2 conversion, which not only add
complexity and increase costs but also lead to a more sulfur sensitive
system. In fact, the sulfur present in the commercially available diesel
fuel could poison the activity of Ag, therefore forcing the system to be
more frequently regenerated and thus to have a higher fuel penalty.

[0013] EP 1 837 076 A1 and JSAE 20077233 disclose a catalyzed soot filter
formulation which suppresses the NO2 formation during active filter
regeneration as well as during normal diesel engine operation. Such
suppression is achieved by the use of mixed base metal oxides e.g. Cu,
La--Cu, Co and Fe oxides comprised in a PGM containing washcoat. Also in
this case, the disadvantages come from the use of such base metal oxides
which render the system more sulfur sensitive or less able to fully
oxidize CO and HC.

[0014] Alternative methods to remove soot and NOx during the engine
operation rely on the use of the so called SCR (selective catalytic
reduction) catalysts, which can be separated from the soot filter or
integrated into it. In both cases, these methods do not provide an
optimal solution which could be widely applied. In fact, while separating
the SCR catalysts from the catalyzed soot filters could be advantageous
to specifically address the abatements of discrete components in the
exhaust system, the increased cost, need of reductant and increased
volume of such a system limits its applicability. On the other side, when
the SCR catalyst is implemented into a catalyzed soot filter, although
the system volume is reduced, there is an increased risk of having
unacceptably high back pressure in the exhaust line as well as still the
need of a reductant to be injected into the system.

[0015] Therefore, it would be desirable to provide an improved catalyzed
soot filter which ensures oxidation of soot via NO2 during normal
diesel engine operation and also suppresses the NO2 formation
reaction during active regeneration. Moreover, it would be desirable to
provide a catalyzed soot filter which ensures that the concentration of
unconverted NO2 exiting the catalyzed soot filter is as low as
possible in order to fulfill the air regulation limits, preferably
without the need of an additional NOx reduction system. Thus, the
catalyzed soot filter should provide an economically more favorable
NO2 abatement. Additionally, it would be desirable to provide a
catalyzed soot filter which, apart from controlling the NO2
formation reaction, continually supports the oxidation and abatement of
CO and unburned HC--and thus allows for a minimum breakthrough of HC and
CO--as well as maintains its soot filtration capabilities. Finally, it
would be desirable to provide a catalyzed soot filter which, due to the
rarity and consequently costs of precious metal components usually used
for the preparation of catalyzed soot filters, contains a reduced amount
of platinum in the catalyst composition allowing for reduced costs for
the catalyzed soot filter without reducing the filter efficiency.

SUMMARY

[0016] Provided according to an aspect of the invention is a catalyzed
soot filter, comprising a wall flow substrate comprising an inlet end, an
outlet end, a substrate axial length extending between the inlet end and
the outlet end, and a plurality of passages defined by internal walls of
the wall flow filter substrate;

wherein the plurality of passages comprise inlet passages having an open
inlet end and a closed outlet end, and outlet passages having a closed
inlet end and an open outlet end; wherein a given inlet passage, an
adjacent outlet passage, and the internal wall between said inlet and
said outlet passage define an overall passage; wherein the internal walls
of at least 20% of the overall passages are at least partially coated
with a first and a second coating; wherein the internal wall of a given
at least partially coated overall passage comprises the first coating
that extends from the open inlet end to a first coating end, thereby
defining a first coating length, wherein the first coating length is x %
of the substrate axial length, with 20≦x≦100; wherein said
internal wall of said overall passage further comprises the second
coating located downstream of the first coating, said second coating
having a second coating length of y % of the substrate axial length, with
20≦y≦100; wherein the first and the second coating overlap
in length by at least 20% of the substrate axial length; wherein the
first coating comprises an oxidation catalyst comprising platinum (Pt)
and optionally palladium (Pd) and wherein the weight ratio of Pt:Pd in
the first coating is in the range of from 1:0 to greater than 1:1;
wherein the second coating comprises an oxidation catalyst comprising Pd
and optionally Pt, wherein the Pt concentration in the second coating is
lower than the Pt concentration in the first coating and wherein the
weight ratio of Pt:Pd in the second coating is in the range of from 1:1
to 0:1; wherein the first coating and the second coating are present on
the wall flow substrate at a coating loading ratio in the range of from
0.25 to 3, calculated as ratio of the loading of the first coating (in
g/inch3 (g/(2.54 cm)3)): loading of the second coating (in
g/inch3 (g/(2.54 cm)3)).

[0017] Further provided in another aspect is a process for manufacturing
such catalyzed soot filter, comprising the steps of [0018] (i) providing
a wall flow substrate, preferably having a porosity in the range of from
38 to 75, determined according to mercury porosity measurement according
to DIN 66133, wherein the wall flow substrate is preferably a cordierite
substrate or a silicon carbide substrate, said wall flow substrate
comprising an inlet end, and outlet end, a substrate axial length
extending between the inlet end and the outlet end, and a plurality of
passages defined by the internal walls of the wall flow substrate;
[0019] wherein the plurality of passages comprise inlet passages having
an open inlet end and a closed outlet end, and outlet passages having a
closed inlet end and an open outlet end; [0020] wherein a given inlet
passage, an adjacent outlet passage, and the internal wall between said
inlet and said outlet passage define an overall passage; [0021] (ii)
applying a first coating to at least part of the internal walls of at
least 20% of the overall passages such that the first coating extends
from the open inlet end to a first coating end whereby a first coating
length is defined, wherein the first coating length is x % of the
substrate axial length, with 20≦x≦100, thereby adjusting
the loading of the first coating to a predetermined value which is
preferably in the range of from 0.05 to 1 g/inch3 (g/(2.54
cm)3), said first coating comprising an oxidation catalyst
comprising platinum (Pt) and optionally palladium (Pd) wherein the weight
ratio of Pt:Pd in the first coating is in the range of from 1:0 to
greater than 1:1; [0022] (iii) applying a second coating to at least part
of the internal walls of said overall passages downstream of the first
coating, said second coating having a second coating length of y % of the
substrate axial length, with 20≦y≦100, so that the first
and the second coating overlap in length by at least 20% of the substrate
axial length; [0023] thereby adjusting the loading of the second coating
to a predetermined value which is preferably in the range of from 0.05 to
1 g/inch3 (g/(2.54 cm)3) such that the first coating and the
second coating are present on the wall flow substrate at a coating
loading ratio in the range of from 0.25 to 3, calculated as ratio of the
loading of the first coating (in g/inch3 (g/(2.54 cm)3)):
loading of the second coating (in g/inch3 (g/(2.54 cm)3)), said
second coating comprising an oxidation catalyst comprising Pd and
optionally Pt, wherein the Pt concentration in the second coating is
lower than the Pt concentration in the first coating and wherein the
weight ratio of Pt:Pd in the second coating is in the range of from 1:1
to 0:1.

[0024] Yet further provided in another aspect is a system for treating a
diesel engine exhaust stream, the system comprising an exhaust conduit in
fluid communication with the diesel engine via an exhaust manifold;
[0025] a catalyzed soot as defined above; and [0026] one or more of the
following in fluid communication with the catalyzed soot filter: a diesel
oxidation catalyst (DOC), a selective catalytic reduction (SCR) article,
a NOx storage and reduction (NSR) catalytic article.

[0027] Still further provided in yet another aspect is a method of
treating a diesel engine exhaust stream, the exhaust stream containing
soot particles, said method comprising contacting the exhaust stream with
a catalyzed soot filter as defined above, preferably after having
directed the exhaust stream through a diesel oxidation catalyst (DOC),
said DOC preferably comprising a flow through substrate or a wall flow
substrate.

BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 shows the NO2/NOx ratios as obtained from the treatment
of diesel exhaust using the catalysed soot filters according to Samples
(A), (B) and (C) of the inventive examples.

DETAILED DESCRIPTION

[0029] An embodiment of the present invention relates to a catalyzed soot
filter, comprising a wall flow substrate comprising an inlet end, an
outlet end, a substrate axial length extending between the inlet end and
the outlet end, and a plurality of passages defined by internal walls of
the wall flow filter substrate;

wherein the plurality of passages comprise inlet passages having an open
inlet end and a closed outlet end, and outlet passages having a closed
inlet end and an open outlet end; wherein a given inlet passage, an
adjacent outlet passage, and the internal wall between said inlet and
said outlet passage define an overall passage; wherein the internal walls
of at least 20% of the overall passages are at least partially coated
with a first and a second coating; wherein the internal wall of a given
at least partially coated overall passage comprises the first coating
that extends from the open inlet end to a first coating end, thereby
defining a first coating length, wherein the first coating length is x %
of the substrate axial length, with 20≦x≦100; wherein said
internal wall of said overall passage further comprises the second
coating located downstream of the first coating, said second coating
having a second coating length of y % of the substrate axial length, with
20≦y≦100; wherein the first and the second coating overlap
in length by at least 20% of the substrate axial length; wherein the
first coating comprises an oxidation catalyst comprising platinum (Pt)
and optionally palladium (Pd) and wherein the weight ratio of Pt:Pd in
the first coating is in the range of from 1:0 to greater than 1:1;
wherein the second coating comprises an oxidation catalyst comprising Pd
and optionally Pt, wherein the Pt concentration in the second coating is
lower than the Pt concentration in the first coating and wherein the
weight ratio of Pt:Pd in the second coating is in the range of from 1:1
to 0:1; wherein the first coating and the second coating are present on
the wall flow substrate at a coating loading ratio in the range of from
0.25 to 3, calculated as ratio of the loading of the first coating (in
g/inch3 (g/(2.54 cm)3)): loading of the second coating (in
g/inch3 (g/(2.54 cm)3)).

[0030] According to an embodiment of the present invention, the internal
walls of at least 20% of the overall passages are at least partially
coated with a first and a second coating. Preferably, the internal walls
of at least 40%, more preferably of at least 60%, and more preferably of
at least 80%, preferably of 100% of the overall passages are at least
partially coated with a first and a second coating.

[0031] According to an embodiment of the present invention, the second
coating may extend from the open inlet end to a second coating end,
thereby defining the second coating length of y % of the substrate axial
length.

[0032] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter defined above, wherein the second coating
extends from the open inlet end to a second coating end, thereby defining
the second coating length of y % of the substrate axial length.

[0033] According to an embodiment of the present invention, the second
coating may extend from the open outlet end to a second coating end,
thereby defining the second coating length of y % of the substrate axial
length.

[0034] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter defined above, wherein the second coating
extends from the open outlet end to a second coating end, thereby
defining the second coating length of y % of the substrate axial length.

[0035] Generally, there are no specific restrictions as far as the first
coating length and the second coating length of the inventive catalyzed
soot filter are concerned provided they are in the ranges defined above,
and the first and the second coating overlap in length by at least 20% of
the substrate axial length. Preferably, the first coating length is from
20 to 80%, more preferably from 20 to 70%, and more preferably from 20 to
60%, more preferably from 20 to 50% of the substrate axial length.

[0036] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter defined above, wherein x is in the range of
from 20 to 80, in particular from 20 to 50. Preferred values of x are,
for example, in the range of from 20-30 or from 25-35 or from 30-40 or
from 35-45 or from 40-50.

[0037] According to an embodiment of the present invention, the first
coating length is x % of the substrate axial length with
20≦x≦100, and the second coating length is y % of the
substrate axial length with 20≦y≦100, wherein the first and
the second coating overlap in length by at least 20% of the substrate
axial length. For example, the first and the second coating overlap in
length by 20, 30 or 40% of the substrate axial length. Preferably, the
first and the second coating overlap in length by 50 to 100%, more
preferably from 60 to 100%, more preferably by 70 to 100%, and more
preferably by 80 to 100%, even more preferably by 90 to 100%, more
preferably by 100% of the substrate axial length.

[0038] According to an embodiment of the present invention, the first
coating comprises an oxidation catalyst comprising Pt an optionally Pd.
While it is generally conceivable that in addition to Pt and optionally
Pd, the first coating further comprises at least one other oxidation
catalyst such as at least one further platinum group metal such as
ruthenium (Ru), rhodium (Rh), osmium (Os), and/or iridium (Ir), it is
particularly preferred that the oxidation catalyst comprised in the first
coating consists of Pt and optionally Pd.

[0039] Further according to an embodiment of the present invention, the
second coating comprises an oxidation catalyst comprising Pd an
optionally Pt. In particular, the Pt concentration in the second coating
is lower than the Pt concentration in the first coating. While it is
generally conceivable that in addition to Pd and optionally Pt, the
second coating further comprises at least one other oxidation catalyst
such as at least one further platinum group metal such as ruthenium (Ru),
rhodium (Rh), osmium (Os), and/or iridium (Ir), it is particularly
preferred that the oxidation catalyst comprised in the second coating
consists of Pd and optionally Pt.

[0040] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter defined above, wherein the oxidation catalyst
comprised in the first coating consists of Pt and optionally Pd and the
oxidation catalyst comprised in the second coating consists of Pd and
optionally Pt wherein the Pt concentration in the second coating is lower
than the Pt concentration in the first coating.

[0041] According to an embodiment of the present invention, the first
coating and the second coating are present on the wall flow substrate at
a coating loading ratio in the range of from 0.25 to 3, calculated as
ratio of the loading of the first coating (in g/inch3 (g/(2.54
cm)3)): loading of the second coating (in g/inch3 (g/(2.54
cm)3)). The term "first coating" as used in this context of an
embodiment of the present invention relates in particular to a washcoat
suitably applied on the internal walls of the inlet passage of a given
overall passage of the wall flow substrate. The term "second coating" as
used in this context of an embodiment of the present invention relates in
particular to a washcoat suitably applied on the internal walls
downstream of the first coating of a given overall passage of the wall
flow substrate. The term "downstream" as used in the context of an
embodiment of the present application means that the second coating is
located on the internal wall of an overall passage with respect to the
first coating so that in region of overlap of first and second coating,
the first coating comes into contact with exhaust gas before the second
coating when the catalyzed soot filter is in operation. Further, the term
"loading" of a given coating as used in the context of an embodiment of
the present invention refers to a loading which is determined by weight
measurement of the wall flow substrate used according to the present
invention before and after having suitably applied the respective
coating, followed by drying and calcination of the catalyzed soot filter
as described hereinunder.

[0042] Preferably, the coating loading ratio of the catalyzed soot filter
of an embodiment of the present invention is in the range of from more
than 0.25 to less than 3, more preferably from 0.6 to 1.5, more
preferably from 0.7 to 1.3, more preferably from 0.75 to 1.25, more
preferably from 0.8 to 1.2, more preferably from 0.85 to 1.15, more
preferably from 0.9 to 1.1, more preferably from 0.95 to 1.05. Thus,
typical preferred values of the coating loading ratio are, for example,
0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, and 1.05.

[0043] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter as defined above, wherein the coating loading
ratio is in the range of from 0.75 to 1.25, preferably from 0.85 to 1.15,
more preferably from 0.95 to 1.05.

[0044] Generally, there are no specific restrictions as far as the loading
of the first coating and the loading of the second coating are concerned.
With the proviso that the coating loading ratio is within above-mentioned
preferred ranges, the loading of the first coating and the loading of the
second coating can be chosen independently from each other. Preferably,
the inventive catalyzed soot filter exhibits a first coating with a
loading in the range of from 0.05 to 1 g/inch3 (g/(2.54 cm)3).
Preferably, the first coating is present with a loading in the range of
from 0.06 to 0.9, more preferably from 0.07 to 0.8, more preferably from
0.08 to 0.7, more preferably from 0.09 to 0.6, and even more preferably
from 0.1 to 0.5 g/inch3 (g/(2.54 cm)3). Even more preferably,
the first coating is present with a loading in the range of from 0.15 to
0.4, more preferably from 0.2 to 0.3 g/inch3 (g/(2.54 cm)3).
Typical values of the loading of the first coating are, for example, 0.20
or 0.22 or 0.24 or 0.25 or 0.26 or 0.28 or 0.30. Preferably, the
inventive catalyzed soot filter exhibits a second coating with a loading
in the range of from 0.05 to 1 g/inch3 (g/(2.54 cm)3).
Preferably, the second coating is present with a loading in the range of
from 0.06 to 0.9, more preferably from 0.07 to 0.8, more preferably from
0.08 to 0.7, more preferably from 0.09 to 0.6, and even more preferably
from 0.1 to 0.5 g/inch3 (g/(2.54 cm)3). Even more preferably,
the second coating is present with a loading in the range of from 0.15 to
0.4, more preferably from 0.2 to 0.3 g/inch3 (g/(2.54 cm)3).
Typical values of the loading of the second coating are, for example,
0.20 or 0.22 or 0.24 or 0.25 or 0.26 or 0.28 or 0.30. It is further
preferred that the loading of the first coating is essentially the same,
more preferably the same as the loading of the second coating.

[0045] Therefore, an embodiment of the present invention relates to the
catalyzed soot filter as defined above, wherein the loading of the first
coating is in the range of from 0.05 to 1, preferably from 0.1 to 0.5,
more preferably from 0.2 to 0.3 g/inch3 (g/(2.54 cm)3), and
wherein the loading of the second coating is in the range of from 0.05 to
1, preferably from 0.1 to 0.5, more preferably from 0.2 to 0.3
g/inch3 (g/(2.54 cm)3).

[0046] According to an embodiment of the present invention, the first
coating comprises an oxidation catalyst comprising platinum (Pt) and
optionally palladium (Pd). Preferably, the oxidation catalyst comprised
in the first coating comprises, even more preferably consists of Pt and
Pd. The weight ratio of Pt:Pd is preferably in the range of from 1:0 to
greater than 1:1, more preferably from 1:0 to 2:1, more preferably from
1:0 to 3:1, more preferably from 1:0 to 4:1, and even more preferably
from 1:0 to 5:1.

[0047] It is further preferred that the oxidation catalyst comprised in
the first coating comprises lower amounts of Pd relative to Pt. It is
conceived that in particular, first coatings are preferred comprising, as
oxidation catalyst, only Pt.

[0048] Therefore, an embodiment of the present inventions also relates to
a catalyzed soot filter wherein in the first coating, the weight ratio of
Pt:Pd is in the range of from 1:0 to greater than 1:1, preferably from
1:0 to 2:1, more preferably from 1:0 to 3:1, more preferably from 1:0 to
4:1, and even more preferably from 1:0 to 5:1, the weight ratio of Pt:Pd
more preferably being 1:0.

[0049] According to an embodiment of the present invention, the second
coating comprises an oxidation catalyst comprising palladium (Pd) and
optionally platinum (Pt). Preferably, the oxidation catalyst comprised in
the second coating comprises, even more preferably consists of Pd and Pt.
The weight ratio of Pt:Pd is preferably in the range of from 1:1 to 0:1,
more preferably from 1:2 to 0:1, more preferably from 1:3 to 0:1, more
preferably from 1:4 to 0:1, and even more preferably from 1:5 to 0:1.

[0050] It is further preferred that the oxidation catalyst comprised in
the second coating comprises lower amounts of Pt relative to Pd. It is
conceived that in particular, second coatings are preferred comprising,
as oxidation catalyst, only Pd.

[0051] Therefore, an embodiment of the present inventions also relates to
a catalyzed soot filter wherein in the second coating, the weight ratio
of Pt:Pd is in the range of from 1:1 to greater than 0:1, preferably from
1:2 to 0:1, more preferably from 1:3 to 0:1, more preferably from 1:4 to
0:1, and even more preferably from 1:5 to 0:1, the weight ratio of Pt:Pd
more preferably being 0:1.

[0052] Generally, the weight ratios of the sum of the weights of Pt and
optionally Pd in the first coating on the one hand and the weights of the
sum of Pd and optionally Pt in the second coating on the other hand can
be suitably chosen provided that the first coating and the second coating
are present on the wall flow substrate at a coating loading ratio in the
range of from 0.25 to 3, calculated as ratio of the loading of the first
coating (in g/inch3 (g/(2.54 cm)3)): loading of the second
coating (in g/inch3 (g/(2.54 cm)3)), or the respective
preferred ranges as defined above, and further provided that the Pt
concentration in the second coating is lower than the Pt concentration in
the first coating. According to the present invention, the weight ratio
of the sum of the weights of Pt and optionally Pd in the first coating to
the sum of the weights of Pd and optionally Pt in the second coating is
in the range of from 1:6 to 10:1.

[0053] Preferably, the weight ratio of the sum of the weights of Pt and
optionally Pd in the first coating relative to the sum of the weights of
Pd and optionally Pt in the second coating is in the range of from 1:6 to
2:1. More preferably, this weight ratio is in the range of from 1:5 to
1.7:1, more preferably from 1:4 to 1.3:1, more preferably from 1:3 to
1:1.

[0054] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter as defined above, wherein the weight ratio of
the sum of the weights of Pt and optionally Pd in the first coating to
the sum of the weights of Pd and optionally Pt in the second coating is
in the range of from 1:6 to 2:1, preferably from 1:3 to 1:1.

[0055] In particular, catalyzed soot filters are preferred which have
first coatings wherein the oxidation catalyst consists of Pt, i.e. first
coatings being free of Pd and platinum group metals other than Pt.
Further, catalyzed soot filters are preferred which have second coatings
wherein the oxidation catalyst consists of Pd, i.e. second coatings being
free of Pt and platinum group metals other than Pd.

[0056] While there are no specific restrictions as far as the Pt
concentration in the first coating is concerned, preferred Pt
concentrations are in the range of from 0.3 to 2 g/ft3 (g/(30.48
cm)3), more preferably from 0.4 to 1.5 g/ft3 (g/(30.48
cm)3), even more preferably from 0.5 to 1 g/ft3 (g/(30.48
cm)3). While there are no specific restrictions as far as the Pd
concentration is concerned, preferred Pd concentrations are in the range
of from 0.3 to 5 g/ft3 (g/(30.48 cm)3), more preferably from
0.4 to 4 g/ft3 (g/(30.48 cm)3), even more preferably from 0.5
to 3 g/ft3 (g/(30.48 cm)3).

[0057] Therefore, an embodiment of the present invention also relates to a
catalyzed soot filter as defined above, wherein in the first coating, the
weight ratio of Pt:Pd is 1:0 and the concentration of Pt is in the range
of from 0.5 to 1 g/ft3 (g/(30.48 cm)3), and wherein in the
second coating, the weight ratio of Pt:Pd is 0:1 and the concentration of
Pd is in the range of from 0.5 to 3 g/ft3 (g/(30.48 cm)3).

[0058] It is further preferred that the weight ratio of the sum of the
weights of Pt and optionally Pd in the first coating relative to the sum
of the weights of Pd and optionally Pt in the second coating is in the
range of from 2.4:1 to 10:1. More preferably, this weight ratio is in the
range of from 2.5:1 to 9.5:1, more preferably from 3:1 to 9:1, more
preferably from 4:1 to 8.5:1, more preferably from 5:1 to 8:1.

[0059] Therefore, an embodiment of the present invention also relates to a
catalyzed soot filter as defined above, wherein the weight ratio of the
sum of the weights of Pt and optionally Pd in the first coating to the
sum of the weight of Pd and optionally Pt in the second coating is in the
range of from 2.4:1 to 10:1, preferably from 5:1 to 8:1.

[0060] In particular, catalyzed soot filters are preferred which have
first coatings wherein the weight ratio of Pt:Pd is in the range of from
1:0 to greater than 1:1 such as, for example, from 50:1 to greater than
1:1 or from 20:1 to greater than 1:1 or from 10:1 to greater than 1:1 or
from 5:1 to greater than 1:1 or from 2:1 to greater than 1:1.

[0061] Further, catalyzed soot filters are preferred which have second
coatings wherein the weight ratio of Pt:Pd is in the range of from 0:1 to
1:1 such as, for example, from 1:50 to 1:1 or from 1:20 to 1:1 or from
1:10 to 1:1 or from 1:5 to 1:1 of from 1:2 to 1.1. Most preferably, the
Pt:Pd weight ratio in the second coating is 0:1.

[0062] While there are no specific restrictions as far as the Pt
concentration in the first coating is concerned, preferred Pt
concentrations are in the range of from 5 to 100 g/ft3 (g/(30.48
cm)3), more preferably from 10 to 60 g/ft3 (g/(30.48
cm)3), even more preferably from 15 to 40 g/ft3 (g/(30.48
cm)3), such as from 20 to 40 g/ft3 (g/(30.48 cm)3) or from
25 to 30 g/ft3 (g/(30.48 cm)3). While there are no specific
restrictions as far as the Pd concentration in the second coating is
concerned, preferred Pd concentrations are in the range of from 1 to 30
g/ft3 (g/(30.48 cm)3), more preferably from 5 to 25/ft3
(g/(30.48 cm)3), even more preferably from 10 to 20 g/ft3
(g/(30.48 cm)3).

[0063] Therefore, an embodiment of the present invention also relates to a
catalyzed soot filter as defined above, wherein in the first coating, the
weight ratio of Pt:Pd is in the range of from 1:0 to greater than 1:1,
preferably 1:0, and the concentration of Pt is in the range of from 5 to
100 g/ft3 (g/(30.48 cm)3), preferably from 10 to 60 g/ft3
(g/(30.48 cm)3), more preferably from 15 to 40 g/ft3 (g/(30.48
cm)3), and wherein in the second coating, the weight ratio of Pt:Pd
is in the range of from 0:1 to 1:1, preferably 0:1, and the concentration
of Pd is in the range of from 1 to 30 g/ft3 (g/(30.48 cm)3),
preferably from 5 to 25 g/ft3 (g/(30.48 cm)3), more preferably
from 10 to 20 g/ft3 (g/(30.48 cm)3).

[0064] Catalyzed soot filters which are especially preferred in the
context of an embodiment of the present invention are characterized in
that the second coating comprises an oxidation catalyst which consists of
Pd and which is free of Pt and also free of platinum group metals other
than Pd and Pt. As to the first coating, it is preferred that apart from
Pt and optionally also Pd, no platinum group metals other than Pt and
optionally Pd are comprised.

[0065] Therefore, an embodiment of the present invention also relates to a
catalyzed soot filter as defined above, wherein the oxidation catalyst
comprised in the first coating consists of Pt and optionally Pd and the
oxidation catalyst comprised in the second coating consists of Pd.

[0066] According to an embodiment of the present invention, the first
coating preferably comprises at least one porous support material for the
respective platinum group metal(s). While there are no specific
restrictions, it is preferred that the porous support material is a
refractory metal oxide. More preferably, the porous support material of
the first coating is selected from the group consisting of alumina,
zirconia, silica, titania, a rare earth metal oxide such as an oxide of
cerium, praseodymium, lanthanum, neodymium, hafnium and samarium,
silica-alumina, alumina-zirconia, alumina-chromia, alumina-rare earth
metal oxide, titania-silica, titania-zirconia, titania-alumina,
ceria-zirconia, and a mixture of two or more thereof. More preferably,
the at least one porous support material is selected from the group
consisting of Al2O3, ZrO2, CeO2, SiO2,
La2O3, Pr6O11, HfO2 and a mixture of tow or more
thereof. Most preferably, the at least one support material comprises a
ceria-zirconia material consisting of CeO2: 45 wt %, ZrO2: 43.5
wt %, La2O3: 8 wt %, Pr6O11: 2 wt %, and HfO2:
1.5 wt %.

[0067] According to an embodiment of the present invention, the second
coating preferably comprises at least one porous support material for the
respective platinum group metal(s). While there are no specific
restrictions, it is preferred that the porous support material is a
refractory metal oxide. More preferably, the porous support material of
the second coating is selected from the group consisting of alumina,
zirconia, silica, titania, a rare earth metal oxide such as an oxide of
cerium, praseodymium, lanthanum, neodymium, hafnium and samarium,
silica-alumina, alumina-zirconia, alumina-chromia, alumina-rare earth
metal oxide, titania-silica, titania-zirconia, titania-alumina,
ceria-zirconia, and a mixture of two or more thereof. More preferably,
the at least one porous support material is selected from the group
consisting of Al2O3, ZrO2, CeO2, SiO2,
La2O3, Pr6O11, HfO2 and a mixture of tow or more
thereof. Most preferably, the at least one support material comprises a
ceria-zirconia material consisting of CeO2: 45 wt %, ZrO2: 43.5
wt %, La2O3: 8 wt %, Pr6O11: 2 wt %, and HfO2:
1.5 wt %.

[0068] Therefore, an embodiment of the present invention also relates to a
catalyzed soot filter as described hereinabove, wherein the first coating
and the second coating comprise at least one porous support material,
wherein the at least one porous support material of the first coating
comprises a ceria-zirconia material consisting of CeO2: 45 wt %,
ZrO2: 43.5 wt %, La2O3: 8 wt %, Pr6O11: 2 wt %,
and HfO2: 1.5 wt %, and wherein the at least one porous support
material of the second coating comprises a ceria-zirconia material
consisting of CeO2: 45 wt %, ZrO2: 43.5 wt %, La2O3:
8 wt %, Pr6O11: 2 wt %, and HfO2: 1.5 wt %.

[0069] According to an embodiment of the present invention, it is further
preferred that the refractory metal oxide of the first coating and/or the
second coating comprises alumina, more preferably gamma alumina or
activated alumina, such as gamma or eta alumina. Preferably, the
activated alumina has a specific surface area, determined according to
BET surface area measurements, of from 60 to 300 m2/g, preferably
from 90 to 200 m2/g, mostly preferred from 100 to 180 m2/g.

[0070] Therefore, an embodiment of the present invention also relates to a
catalyzed soot filter as defined above, wherein the support material of
the first coating comprises Al2O3, preferably
gamma-Al2O3, and wherein the support material of the second
coating comprises Al2O3, preferably gamma-Al2O3.

[0072] The zeolite can be a natural or synthetic zeolite such as
faujasite, chabazite, clinoptilolite, mordenite, silicalite, zeolite X,
zeolite Y, ultrastable zeolite Y, ZSM-5 zeolite, ZSM-12 zeolite, SSZ-3
zeolite, SAPO 5 zeolite, offretite, or a beta zeolite. Preferred zeolite
materials have a high silica to alumina ratio. The zeolites may have a
silica/alumina molar ratio of from at least 25/1, preferably at least
50/1, with useful ranges of from 25/1 to 1000/1, 50/1 to 500/1 as well as
25/1 to 300/1, from 100/1 to 250/1, or alternatively from 35/1 to 180/1
is also exemplified. Preferred zeolites include ZSM, Y and beta zeolites.
A particularly preferred beta zeolite is of the type disclosed in U.S.
Pat. No. 6,171,556.

[0073] Wall flow substrates useful for the catalyzed soot filter of an
embodiment of the present invention have a plurality of fine,
substantially parallel flow passages extending along the longitudinal
axis of the substrate. Each passage is blocked at one end of the
substrate body, with alternate passages blocked at opposite end-faces.
Such monolithic carriers may contain up to about 400 flow passages (or
"cells") per square inch ((2.54 cm)2) of cross section, although far
fewer may be used. For example, the carrier may have from 7 to 400,
preferably from 100 to 400, cells per square inch ("cpsi"). The cells can
have cross sections that are rectangular, square, circular, oval,
triangular, hexagonal, or are of other polygonal shapes.

[0074] Preferred wall flow substrates are composed of ceramic-like
materials such as cordierite, alpha-alumina, silicon carbide, silicon
nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or
zirconium silicate, or of refractory metals such as stainless steel.
Preferred wall flow substrates are formed from cordierite and silicon
carbide. Such materials are able to withstand the environment,
particularly high temperatures, encountered in treating the exhaust
streams. Ceramic wall flow substrates are typically formed of a material
having a porosity of about 40 to 70. The term "porosity" as used in this
context is understood as being determined according to mercury porosity
measurement according to DIN 66133. According to the present invention,
wall flow substrates are preferred having a porosity in the range from 38
to 75.

[0075] Therefore, an embodiment of the present invention also relates to a
catalyzed soot filter as defined above, wherein the wall flow substrate
has a porosity in the range of from 38 to 75, determined according to
mercury porosity measurement according to DIN 66133, wherein the wall
flow substrate is preferably a cordierite substrate or a silicon carbide
substrate.

[0076] For instance, a wall flow substrate having a porosity of 55-65 and
a mean pore diameter of about 15-25 microns provide adequate exhaust
flow. Preferred configurations use wall flow substrates with 100 cpsi
that have a 17 mil wall (1 mil corresponds to 0.0254 mm), and wall flow
substrates with 300 cpsi and a 12-14 mil wall.

[0077] Generally, there are no restrictions as to the substrate axial
lengths of the catalyzed soot filter of the present invention. Substrate
axial lengths will mainly depend on the intended use of the catalyzed
soot filter of the present invention. Typical substrate axial lengths of
catalyzed soot filter used, for example, in the automotive area are in
the range of from 4 to 10 inches (10.16 cm to 25.4 cm), preferably from 6
to 8 inches (15.24 cm to 20.32 cm).

[0078] Each of the coatings of an embodiment of the present invention
present on the wall flow substrate is formed from a respective washcoat
composition that contains the at least one porous support material as
described above. Other additives such as binders and stabilizers can also
be included in the washcoat composition. Such stabilizers can be included
in either the first coating or in the second coating or in both first and
second coatings, as described hereinunder. As disclosed in U.S. Pat. No.
4,727,052, porous support materials, such as activated alumina, can be
thermally stabilized to retard undesirable alumina phase transformations
from gamma to alpha at elevated temperatures. Stabilizers can be selected
from at least one alkaline earth metal components selected from the group
consisting of magnesium, barium, calcium and strontium, preferably
strontium and barium. When present, stabilizers materials are added at
from about 0.01 g/in3 (g/(2.54 cm)3) to 0.15 g/in3
(g/(2.54 cm)3) in the coating.

[0079] A given coating is disposed on the surface of the internal walls.
Further, it is conceivable that a given coating is disposed on another
coating which had been applied onto the surface of the internal walls or
onto yet another coating. Further, a given coating may partially permeate
the porous internal walls or the coating onto which it is applied.

[0080] For the preparation of the washcoat composition to be applied onto
the internal walls of the wall flow substrate, it is preferred to
disperse a suitable Pt and/or Pd component precursor on a suitable porous
support material, preferably a suitable refractory metal oxide as
described hereinabove. More preferably, a water-soluble or
water-dispersible Pt and/or Pd component precursor is/are impregnated on
a suitable porous support material, preferably a suitable refractory
metal oxide, followed by drying and fixing steps. Suitable Pt and/or Pd
component precursors include, for example, potassium platinum chloride,
ammonium platinum thiocyanate, amine-solubilized platinum hydroxide,
chloroplatinic acid, palladium nitrate, and the like. Other suitable
precursors will be apparent to those of skill in the art. The impregnated
support material is preferably dried with the Pt and/or Pd component
fixed thereon. Generally, drying temperatures are in the range from 60 to
250° C., preferably from 90 to 210° C., more preferably
from 100 to 150° C. Drying can be carried out in any suitable
atmosphere, with N2 or air being preferred. After drying, it is
preferred to finally fix the Pt and/or Pd component on the support
material by suitable calcination and/or other suitable methods such as
treatment with acetic acid. In general, any method resulting in the Pt
and/or Pd component being in water-insoluble form is suitable. Generally,
calcination temperatures are in the range from 250 to 800° C.,
preferably from 350 to 700° C., more preferably from 400 to
600° C. Calcination can be carried out in any suitable atmosphere,
with N2 or air being preferred. By, for example, calcination, the
catalytically active elemental Pt and/or Pd or the respective oxide is
obtained. It is to be understood that the term "Pt component" or "Pd
component" present in the finally obtained catalyzed soot filter as used
in the context of the present invention relates to the Pt and/or Pd
component in the form of the catalytically active elemental Pt and/or Pd,
or the oxide thereof, or the mixture of elemental Pt and/or Pd and the
oxide thereof.

[0081] Therefore, an embodiment of the present invention also relates to a
process for manufacturing a catalyzed soot filter as defined above, the
process comprising the steps of [0082] (i) providing a wall flow
substrate, preferably having a porosity in the range of from 38 to 75,
determined according to mercury porosity measurement according to DIN
66133, wherein the wall flow substrate is preferably a cordierite
substrate or a silicon carbide substrate, said wall flow substrate
comprising an inlet end, and outlet end, a substrate axial length
extending between the inlet end and the outlet end, and a plurality of
passages defined by the internal walls of the wall flow substrate;
[0083] wherein the plurality of passages comprise inlet passages having
an open inlet end and a closed outlet end, and outlet passages having a
closed inlet end and an open outlet end; [0084] wherein a given inlet
passage, an adjacent outlet passage, and the internal wall between said
inlet and said outlet passage define an overall passage; [0085] (ii)
applying a first coating to at least part of the internal walls of at
least 20% of the overall passages such that the first coating extends
from the open inlet end to a first coating end whereby a first coating
length is defined, wherein the first coating length is x % of the
substrate axial length, with 20≦x≦100, thereby adjusting
the loading of the first coating to a predetermined value which is
preferably in the range of from 0.05 to 1 g/inch3 (g/(2.54
cm)3), said first coating comprising an oxidation catalyst
comprising platinum (Pt) and optionally palladium (Pd) wherein the weight
ratio of Pt:Pd in the first coating is in the range of from 1:0 to
greater than 1:1; [0086] (iii) applying a second coating to at least part
of the internal walls of said overall passages downstream of the first
coating, said second coating having a second coating length of y % of the
substrate axial length, with 20≦y≦100, so that the first
and the second coating overlap in length by at least 20% of the substrate
axial length; [0087] thereby adjusting the loading of the second coating
to a predetermined value which is preferably in the range of from 0.05 to
1 g/inch3 (g/(2.54 cm)3) such that the first coating and the
second coating are present on the wall flow substrate at a coating
loading ratio in the range of from 0.25 to 3, calculated as ratio of the
loading of the first coating (in g/inch3 (g/(2.54 cm)3)):
loading of the second coating (in g/inch3 (g/(2.54 cm)3)), said
second coating comprising an oxidation catalyst comprising Pd and
optionally Pt, wherein the Pt concentration in the second coating is
lower than the Pt concentration in the first coating and wherein the
weight ratio of Pt:Pd in the second coating is in the range of from 1:1
to 0:1.

[0088] According to an embodiment of the present invention, step (iii) may
be carried out before step (ii) whereby the second coating is applied
such that it extends from the open inlet end to a second coating end,
thereby defining the second coating length of y % of the substrate axial
length.

[0089] Therefore, an embodiment of the present invention also relates to a
process for manufacturing a catalyzed soot filter as defined above,
wherein step (iii) is carried out before step (ii) and wherein the second
coating is applied such that it extends from the open inlet end to a
second coating end, thereby defining the second coating length of y % of
the substrate axial length.

[0090] According to an embodiment of the present invention, step (iii) may
be carried out before, simultaneously with or after step (ii) whereby the
second coating is applied such that it extends from the open outlet end
to a second coating end, thereby defining the second coating length of y
% of the substrate axial length.

[0091] Therefore, an embodiment of the present invention also relates to a
process for manufacturing a catalyzed soot filter as defined above,
wherein step (iii) is carried out before, simultaneously with or after
step (ii) and wherein the second coating is applied such that it extends
from the open outlet end to a second coating end, thereby defining the
second coating length of y % of the substrate axial length.

[0092] Preferred values of the ranges, lengths, concentrations and the
like, as far as the inventive catalyzed soot filters are concerned, are
as defined above.

[0093] The catalyzed soot filter of an embodiment of the present invention
can be used in an integrated emission treatment system, in particular in
an exhaust conduit comprising one or more additional components for the
treatment of diesel exhaust emissions. For example, such exhaust conduit
which is most preferably in fluid communication with the diesel engine
may comprise a catalyzed soot filter according to the present invention
and may further comprise a diesel oxidation catalyst (DOC) article and/or
a selective catalytic reduction (SCR) article and/or an NOx storage and
reduction (NSR) catalytic article. Most preferably, the DOC article
and/or the SCR article and/or the NSR article are in fluid communication
with the catalyzed soot filter. The diesel oxidation catalyst can be
located upstream or downstream from the catalyzed soot filter and/or
selective catalytic reduction component. More preferably, the catalyzed
soot filter of the present invention is located downstream from the DOC
article. Still more preferably the catalyzed soot filter of the present
invention is located either upstream or downstream of the SCR article.

[0094] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter as defined above, comprised in a system for
treating a diesel engine exhaust stream, the system further comprising an
exhaust conduit in fluid communication with the diesel engine via an
exhaust manifold, and further comprising one or more of the following in
fluid communication with the catalyzed soot filter: a diesel oxidation
catalyst (DOC), a selective catalytic reduction (SCR) article, an NOx
storage and reduction (NSR) catalytic article.

[0095] Even more preferably, downstream the inventive catalyzed soot
filter, there is no NOx reduction catalytic article comprised in the
system, preferably no NOx storage and reduction (NSR) catalytic article.

[0096] A suitable SCR article for use in the exhaust conduit is typically
able to catalyze the reaction of O2 with any excess NH3 to
N2 and H2O, so that NH3 is not emitted to the atmosphere.
Useful SCR catalyst compositions used in the exhaust conduit should also
have thermal resistance to temperatures greater than 650° C. Such
high temperatures may be encountered during regeneration of the upstream
catalyzed soot filter. Suitable SCR articles are described, for instance,
in U.S. Pat. No. 4,961,917 and U.S. Pat. No. 5,516,497. Suitable SCR
articles include one or both of an iron and a copper promoter typically
present in a zeolite in an amount of from about 0.1 to 30 percent by
weight, preferably from about 1 to 5 percent by weight, of the total
weight of promoter plus zeolite. Typical zeolites may exhibit a CHA
framework structure.

[0097] According to an embodiment of the present invention, the inventive
catalyzed soot filter is preferably arranged downstream of the DOC. In
such an arrangement, the inventive catalyzed soot filter provides the
advantage that HC and CO are reduced during soot combustion which is most
preferably achieved by the upstream zone of the inventive filter.
Further, the specific design of the rear zone ensures that in the
downstream zone of the catalyzed soot filter, as low an amount of NOx as
possible is generated. Thus, downstream such DOC, it was found that the
inventive catalyzed soot filter is very advantageous in its clean-up
function for the treatment of diesel exhaust.

[0098] Therefore, an embodiment of the present invention also relates to
the catalyzed soot filter as defined above, comprised in a system for
treating a diesel engine exhaust stream, the system further comprising an
exhaust conduit in fluid communication with the diesel engine via an
exhaust manifold, and further comprising a diesel oxidation catalyst
wherein the catalyzed soot filter is arranged downstream of the DOC.

[0099] Also, an embodiment of the present invention relates to the
catalyzed soot filter as defined above for use in a method of treating a
diesel engine exhaust stream, the exhaust stream containing soot
particles, said method comprising contacting the exhaust stream with the
catalyzed soot filter, preferably after having directed the exhaust
stream through a diesel oxidation catalyst (DOC), said DOC preferably
comprising a flow through substrate or a wall flow substrate. Similarly,
an embodiment of the present invention relates to the use of the
catalyzed soot filter as defined above for treating a diesel engine
exhaust stream, the exhaust stream containing soot particles, wherein the
exhaust stream is contacted with the catalyzed soot filter, preferably
after having directed the exhaust stream through a diesel oxidation
catalyst (DOC), said DOC preferably comprising a flow through substrate
or a wall flow substrate.

[0100] Further, an embodiment of the present invention relates to a system
for treating for treating a diesel engine exhaust stream, the system
comprising an exhaust conduit in fluid communication with the diesel
engine via an exhaust manifold; a catalyzed soot filter as defined above;
and one or more of the following in fluid communication with the
catalyzed soot filter: a diesel oxidation catalyst (DOC), a selective
catalytic reduction (SCR) article, a NOx storage and reduction (NSR)
catalytic article.

[0101] Preferably, in this system, the catalyzed soot filter is arranged
downstream of the DOC. More preferably, the system does not contain a NOx
reduction catalytic article, and more preferably, the system does not
contain a NOx storage and reduction (NSR) catalytic article.

[0102] Therefore, an embodiment of the present invention also relates to a
method of treating a diesel engine exhaust stream, the exhaust stream
containing soot particles, said method comprising contacting the exhaust
stream with a catalyzed soot filter as defined above, preferably after
having directed the exhaust stream through a diesel oxidation catalyst
(DOC), said DOC preferably comprising a flow through substrate or a wall
flow substrate.

[0103] According to an embodiment of the present invention, this method
optionally further comprises directing the exhaust stream resulting from
the DOC or from the catalyzed soot filter through a selective catalytic
reduction (SCR) article.

[0104] The present invention include the following embodiments, wherein
these include the specific combinations of embodiments as indicated by
the respective interdependencies defined therein: [0105] 1. A catalyzed
soot filter, comprising [0106] a wall flow substrate comprising an inlet
end, an outlet end, a substrate axial length extending between the inlet
end and the outlet end, and a plurality of passages defined by internal
walls of the wall flow filter substrate; [0107] wherein the plurality of
passages comprise inlet passages having an open inlet end and a closed
outlet end, and outlet passages having a closed inlet end and an open
outlet end; [0108] wherein a given inlet passage, an adjacent outlet
passage, and the internal wall between said inlet and said outlet passage
define an overall passage; [0109] wherein the internal walls of at least
20% of the overall passages are at least partially coated with a first
and a second coating; [0110] wherein the internal wall of a given at
least partially coated overall passage comprises the first coating that
extends from the open inlet end to a first coating end, thereby defining
a first coating length, wherein the first coating length is x % of the
substrate axial length, with 20≦x≦100; [0111] wherein said
internal wall of said overall passage further comprises the second
coating located downstream of the first coating, said second coating
having a second coating length of y % of the substrate axial length, with
20≦y≦100; [0112] wherein the first and the second coating
overlap in length by at least 20% of the substrate axial length; [0113]
wherein the first coating comprises an oxidation catalyst comprising
platinum (Pt) and optionally palladium (Pd) and wherein the weight ratio
of Pt:Pd in the first coating is in the range of from 1:0 to greater than
1:1; [0114] wherein the second coating comprises an oxidation catalyst
comprising Pd and optionally Pt, wherein the Pt concentration in the
second coating is lower than the Pt concentration in the first coating
and wherein the weight ratio of Pt:Pd in the second coating is in the
range of from 1:1 to 0:1; [0115] wherein the first coating and the second
coating are present on the wall flow substrate at a coating loading ratio
in the range of from 0.25 to 3, calculated as ratio of the loading of the
first coating (in g/inch3 (g/(2.54 cm)3)): loading of the
second coating (in g/inch3 (g/(2.54 cm)3)). [0116] 2. The
catalyzed soot filter according to embodiment 1, wherein the second
coating extends from the open inlet end to a second coating end, thereby
defining the second coating length of y % of the substrate axial length.
[0117] 3. The catalyzed soot filter according to embodiment 1, wherein
the second coating extends from the open outlet end to a second coating
end, thereby defining the second coating length of y % of the substrate
axial length.4. The catalyzed soot filter of any of embodiments 1 to 3,
wherein x is in the range of from 20 to 80, preferably from 20 to 50.
[0118] 5. The catalyzed soot filter of any of embodiments 1 to 4, wherein
the coating loading ratio is in the range of from 0.75 to 1.25,
preferably from 0.85 to 1.15, more preferably from 0.95 to 1.05. [0119]
6. The catalyzed soot filter of any of embodiment 1 to 5, wherein the
loading of the first coating is in the range of from 0.05 to 1,
preferably from 0.1 to 0.5, more preferably from 0.2 to 0.3 g/inch3
(g/(2.54 cm)3), and wherein the loading of the second coating is in
the range of from 0.05 to 1, preferably from 0.1 to 0.5, more preferably
from 0.2 to 0.3 g/inch3 (g/(2.54 cm)3). [0120] 7. The catalyzed
soot filter of any of embodiments 1 to 6, wherein in the first coating,
the weight ratio of Pt:Pd is in the range of from 1:0 to 2:1, preferably
from 1:0 to 5:1. [0121] 8. The catalyzed soot filter of any of
embodiments 1 to 7, wherein in the first coating, the weight ratio of
Pt:Pd is 1:0. [0122] 9. The catalyzed soot filter of any of embodiments 1
to 8, wherein in the second coating, the weight ratio of Pt:Pd is in the
range of from 1:2 to 0:1, preferably from 1:5 to 0:1. [0123] 10. The
catalyzed soot filter of any of embodiments 1 to 9, wherein in the second
coating, the weight ratio of Pt:Pd is 0:1. [0124] 11. The catalyzed soot
filter of any of embodiments 1 to 10, wherein the weight ratio of the sum
of the weights of Pt and optionally Pd in the first coating to the sum of
the weights of Pd and optionally Pt in the second coating is in the range
of from 1:6 to 10:1. [0125] 12. The catalyzed soot filter of embodiment
11, wherein the weight ratio of the sum of the weights of Pt and
optionally Pd in the first coating to the sum of the weights of Pd and
optionally Pt in the second coating is in the range of from 1:6 to 2:1,
preferably from 1:3 to 1:1. [0126] 13. The catalyzed soot filter of
embodiment 12, wherein in the first coating, the weight ratio of Pt:Pd is
1:0 and the concentration of Pt is in the range of from 0.5 to 1
g/ft3 (g/(30.48 cm)3), and wherein in the second coating, the
weight ratio of Pt:Pd is 0:1 and the concentration of Pd is in the range
of from 0.5 to 3 g/ft3 (g/(30.48 cm)3). [0127] 14. The
catalyzed soot filter of embodiment 11, wherein the weight ratio of the
sum of the weights of Pt and optionally Pd in the first coating to the
sum of the weights of Pd and optionally Pt in the second coating is in
the range of from 2.4:1 to 10:1, preferably from 5:1 to 8:1. [0128] 15.
The catalyzed soot filter of embodiment 14, wherein in the first coating,
the weight ratio of Pt:Pd is in the range of from 1:0 to 1:1, preferably
1:0, and the concentration of Pt is in the range of from 5 to 100
g/ft3 (g/(30.48 cm)3), preferably from 10 to 60 g/ft3
(g/(30.48 cm)3), more preferably from 15 to 40 g/ft3 (g/(30.48
cm)3), and wherein in the second coating, the weight ratio of Pt:Pd
is in the range of from 0:1 to 1:1, preferably 0:1, and the concentration
of Pd is in the range of from 1 to 30 g/ft3 (g/(30.48 cm)3),
preferably from 5 to 25 g/ft3 (g/(30.48 cm)3), more preferably
from 10 to 20 g/ft3 (g/(30.48 cm)3). [0129] 16. The catalyzed
soot filter of any of embodiments 1 to 15, wherein the oxidation catalyst
comprised in the first coating consists of Pt and optionally Pd and the
oxidation catalyst comprised in the second coating consists of Pd. [0130]
17. The catalyzed soot filter of any of embodiments 1 to 16, wherein the
first coating and the second coating comprise at least one porous support
material for the respective platinum group metal(s), wherein the at least
one porous support material of the first coating comprises a
ceria-zirconia material consisiting of CeO2: 45 wt %, ZrO2:
43.5 wt %, La2O3: 8 wt %, Pr6O11: 2 wt %, and
HfO2: 1.5 wt %, and wherein the at least one porous support material
of the second coating comprises a ceria-zirconia material consisting of
CeO2: 45 wt %, ZrO2: 43.5 wt %, La2O3: 8 wt %,
Pr6O11: 2 wt %, and HfO2: 1.5 wt %. [0131] 18. The
catalyzed soot filter of embodiment 17, wherein the support material of
the first coating comprises Al2O3, preferably
gamma-Al2O3, and wherein the support material of the second
coating comprises Al2O3, preferably gamma-Al2O3.
[0132] 19. The catalyzed soot filter of any of embodiments 1 to 18,
wherein the wall flow substrate has a porosity in the range of from 38 to
75, determined according to mercury porosity measurement according to DIN
66133, wherein the wall flow substrate is preferably a cordierite
substrate or a silicon carbide substrate. [0133] 20. The catalyzed soot
filter of any of embodiments 1 to 19, comprised in a system for treating
a diesel engine exhaust stream, the system further comprising an exhaust
conduit in fluid communication with the diesel engine via an exhaust
manifold, and further comprising one or more of the following in fluid
communication with the catalyzed soot filter: a diesel oxidation catalyst
(DOC), a selective catalytic reduction (SCR) article, an NOx storage and
reduction (NSR) catalytic article. [0134] 21. The catalyzed soot filter
of embodiment 20, arranged downstream of the DOC. [0135] 22. The
catalyzed soot filter of any of embodiments 1 to 21 for use in a method
of treating a diesel engine exhaust stream, the exhaust stream containing
soot particles, said method comprising contacting the exhaust stream with
the catalyzed soot filter, preferably after having directed the exhaust
stream through a DOC, said DOC preferably comprising a flow through
substrate or a wall flow substrate. [0136] 23. A process for
manufacturing a catalyzed soot filter of any of embodiments 1 to 19,
comprising the steps of [0137] (i) providing a wall flow substrate,
preferably having a porosity in the range of from 38 to 75, determined
according to mercury porosity measurement according to DIN 66133, wherein
the wall flow substrate is preferably a cordierite substrate or a silicon
carbide substrate, said wall flow substrate comprising an inlet end, and
outlet end, a substrate axial length extending between the inlet end and
the outlet end, and a plurality of passages defined by the internal walls
of the wall flow substrate; [0138] wherein the plurality of passages
comprise inlet passages having an open inlet end and a closed outlet end,
and outlet passages having a closed inlet end and an open outlet end;
[0139] wherein a given inlet passage, an adjacent outlet passage, and the
internal wall between said inlet and said outlet passage define an
overall passage; [0140] (ii) applying a first coating to at least part
of the internal walls of at least 20% of the overall passages such that
the first coating extends from the inlet end to a first coating end
whereby a first coating length is defined, wherein the first coating
length is x % of the substrate axial length, with 20≦x≦100,
thereby adjusting the loading of the first coating to a predetermined
value which is preferably in the range of from 0.05 to 1 g/inch3
(g/(2.54 cm)3), said first coating comprising an oxidation catalyst
comprising platinum (Pt) and optionally palladium (Pd) wherein the weight
ratio of Pt:Pd in the first coating is in the range of from 1:0 to
greater than 1:1; [0141] (iii) applying a second coating to at least part
of the internal walls of said overall passages downstream of the first
coating, said second coating having a second coating length of y % of the
substrate axial length, with 20≦y≦100, so that the first
and the second coating overlap in length by at least 20% of the substrate
axial length; [0142] thereby adjusting the loading of the second coating
to a predetermined value which is preferably in the range of from 0.05 to
1 g/inch3 (g/(2.54 cm)3) such that the first coating and the
second coating are present on the wall flow substrate at a coating
loading ratio in the range of from 0.25 to 3, calculated as ratio of the
loading of the first coating (in g/inch3 (g/(2.54 cm)3)):
loading of the second coating (in g/inch3 (g/(2.54 cm)3)), said
second coating comprising an oxidation catalyst comprising Pd and
optionally Pt, wherein the Pt concentration in the second coating is
lower than the Pt concentration in the first coating and wherein the
weight ratio of Pt:Pd in the second coating is in the range of from 1:1
to 0:1. [0143] 24. The process of embodiment 23, wherein step (iii)
is carried out before step (ii) and wherein the second coating is applied
such that it extends from the open inlet end to a second coating end,
thereby defining the second coating length of y % of the substrate axial
length. [0144] 25. The process of embodiment 23, wherein step (iii) is
carried out before, simultaneously with or after step (ii) and wherein
the second coating is applied such that it extends from the open outlet
end to a second coating end, thereby defining the second coating length
of y % of the substrate axial length. [0145] 26. A system for treating a
diesel engine exhaust stream, the system comprising an exhaust conduit in
fluid communication with the diesel engine via an exhaust manifold;
[0146] a catalyzed soot filter of any of embodiments 1 to 19; and [0147]
one or more of the following in fluid communication with the catalyzed
soot filter: a diesel oxidation catalyst (DOC), a selective catalytic
reduction (SCR) article, a NOx storage and reduction (NSR) catalytic
article. [0148] 27. The system of embodiment 26, wherein the catalyzed
soot filter is arranged downstream of the DOC. [0149] 28. A method of
treating a diesel engine exhaust stream, the exhaust stream containing
soot particles, said method comprising contacting the exhaust stream with
a catalyzed soot filter of any of embodiments 1 to 19, preferably after
having directed the exhaust stream through a diesel oxidation catalyst
(DOC), said DOC preferably comprising a flow through substrate or a wall
flow substrate. [0150] 29. The method of embodiment 28, further
comprising directing the exhaust stream resulting from the DOC or from
the catalyzed soot filter through a selective catalytic reduction (SCR)
article.

[0151] In the following, embodiments of the present invention is further
illustrated by the following examples.

[0153] For the first coating gamma-alumina (final dry content 0.15
g/in3) was impregnated with a Platinum solution with Platinum as an
ammine stabilized Pt complex to give a dry solids content of Pt of 25
g/ft3 followed by an impregnation of an aqueous solution of
Palladium nitrate giving a dry solids content of Pd of 5 g/ft3. The
resulting powder was dispersed in water, and H-Beta zeolite was added as
dry powder resulting in a dry solids content of 0.15 g/in3.
Subsequently, the resulting slurry was used for coating the silicon
carbide filter substrate (2.5 L volume) from the open inlet side to 50%
of the total filter length. After drying at 110° C. in air and
calcination at 450° C. in air the amount of washcoat on the 50%
inlet of the filter substrate were approximately 0.37 g/in3.

[0154] For the second coating 100% ceria (dry solids content 0.15
g/in3) was impregnated with an aqueous solution of Palladium nitrate
giving a dry solids content of Pd of 20 g/ft3. The resulting powder
was dispersed in water, and gamma-alumina was added as dry powder
resulting in a dry solids content of 0.15 g/in3. Subsequently, the
resulting slurry was used for coating the silicon carbide filter
substrate (2.5 L volume) from the open outlet side to 50% of the total
filter length. After drying at 110° C. in air and calcination at
450° C. in air the amount of washcoat on the 50% outlet of the
filter substrate were approximately 0.36 g/in3.

[0155] For the first coating gamma-alumina (dry solids content 0.15
g/in3) was impregnated with a Platinum solution with Platinum as an
ammine stabilized Pt complex to give a dry solids content of Pt of 25
g/ft3 followed by an impregnation of an aqueous solution of
Palladium nitrate giving a dry solids content of Pd of 5 g/ft3. The
resulting powder was dispersed in water resulting in a dry solids content
of 0.15 g/in3. Subsequently, the resulting slurry was used for
coating the silicon carbide filter substrate (2.5 L volume) from the open
inlet side to 50% of the total filter length. After drying at 110°
C. in air and calcination at 450° C. in air the amount of washcoat
on the 50% inlet of the filter substrate were approximately 0.22
g/in3.

[0156] For the second coating ceria-zirconia material (CeO2: 45 wt %,
ZrO2: 43.5 wt %, La2O3: 8 wt %, Pr6O11: 2 wt %,
HfO2: 1.5 wt %, dry solids content 0.05 g/in3) was impregnated
with an aqueous solution of Palladium nitrate giving a dry solids content
of Pd of 10 g/ft3. The resulting powder was dispersed in water, and
H-Beta zeolite and gamma-alumina were added as dry powder resulting in a
dry solids content of 0.05 g/in3. Subsequently, the resulting slurry
was used for coating the silicon carbide filter substrate (2.5 L volume)
from the open outlet side to 100% of the total filter length. After
drying at 110° C. in air and calcination at 450° C. in air
the amount of washcoat on the 100% outlet of the filter substrate were
approximately 0.26 g/in3.

[0157] For the first coating gamma-alumina (dry solids content 0.15
g/in3) was impregnated with a Platinum solution with Platinum as an
ammine stabilized Pt complex to give a dry solids content of Pt of 12.5
g/ft3 followed by an impregnation of an aqueous solution of
Palladium nitrate giving a dry solids content of Pd of 2.5 g/ft3.
The resulting powder was dispersed in water. Subsequently, the resulting
slurry was used for coating the silicon carbide filter substrate (2.5 L
volume) from the open inlet side to 100% of the total filter length.
After drying at 110° C. air and calcination at 450° C. in
air the amount of washcoat on the 100% inlet of the filter substrate were
approximately 0.21 g/in3.

[0158] For the second coating ceria-zirconia material (CeO2: 45 wt %,
ZrO2: 43.5 wt %, La2O3: 8 wt %, Pr6O11: 2 wt %,
HfO2: 1.5 wt %, dry solids content 0.05 g/in3) was impregnated
with an aqueous solution of Palladium nitrate giving a dry solids content
of Pd of 10 g/ft3. The resulting powder was dispersed in water, and
H-Beta zeolite and gamma-alumina were added as dry powder resulting in a
dry solids content of 0.05 g/in3. Subsequently, the resulting slurry
was used for coating the silicon carbide filter substrate (2.5 L volume)
from the open outlet side to 100% of the total filter length. After
drying at 110° C. air and calcination at 450° C. in air the
amount of washcoat on the 100% outlet of the filter substrate were
approximately 0.26 g/in3.

2. Comparison to State of the Art Catalyst Technologies with Invention
Technology (Light-off Test)

[0168] Samples A, B, and C were tested for NO2 light-off performance.
Prior to testing the samples were hydrothermally aged in an oven at
750° C. for 5 h in air with 10% of water. For light-off testing
each sample was placed upstream behind a state of the art Pt/Pd=1/1 DOC
with 120 g/ft3 loading and 1.2 L catalyst volume downstream in the
exhaust line a 4 cylinder light duty common rail diesel engine with 2 L
engine displacement. The CO, HC, NOx and NO concentration in the exhaust
stream was 600 ppm, 60 ppm (C3 basis), 100 ppm and 50 ppm, respectively.
The gas flow under standard conditions was around 45 m3/h. The
temperature ramp was 5 K/min. The NO2/NOx ratio at 300° C.
pre CSF temperature was used for evaluation. A lower NO2/NOx ratio
at 300° C. relates to a lower NO2 formation during driving.

[0169] The NO2/NOx ratio at 300° C. during light-off Samples
(A) to (C) is shown in FIG. 1.

[0170] Samples B and C showed lower maximum NO2/NOx ratio compared to
Sample A and therefore a lower NO2 tail pipe emission during
driving. The lowest NO2/NOx ratio is observed for Sample C with the
100% overlap of the first and second coat.